Basic row removal

Added in row removal that works fine with single rows at a time. If the
user invokes the removal of two rows then the algorithm sometimes fails
- this needs to be fixed. Also started adding in a basic UI, sort of
gave up after a while but I will come back to it later on.
I have also noticed some glitches with a few of the Tetrimino pieces not
rotating properly, I need to look into this.